Field of the Invention
The present invention relates to an electrophotographic image forming apparatus for forming an image on a roll sheet.
Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a uniformly-charged photoconductor (for example, a photoconductor drum) with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet through an intermediate transfer belt, followed by heating and pressurization for fixing, whereby an image is formed on the sheet.
It is known that sheets are conveyed in a tilted state (so-called skew or meandering) in such an image forming apparatus due to a slight inclination of a conveyance roller shaft, a difference in a nip pressure (hereinafter referred to as “conveyance nip pressure”) between a plurality of roller pairs in the sheet feeding path section, or other reasons. In particular, when the meandering occurs during image formation on a roll sheet, the sheet is continuously conveyed through a conveyance nip in a tilted state, and consequently, not only deviation of the image formation region, but also damages such as paper wrinkle may possibly be caused. Conventionally, the meandering of a roll sheet is prevented by pushing the guide member from the both sides of the roll sheet in the sheet width direction (the direction orthogonal to the sheet conveyance direction) (for example, PTL 1: Japanese Patent Application Laid-Open No. 2006-188352).
However, since a guide member is fixed at a position set in advance, the technique disclosed in PTL 1 has the following problem. For example, when a roll sheet shrinks during a fixing process in image formation on the roll sheet, a gap is formed between a guide member and a roll sheet whose positions are set in advance, and thus the meandering which occurs after the fixation is facilitated. In addition, for example, when a roll sheet expands during a fixation process, the width of the roll sheet becomes larger than the guide width of the guide member whose position is set in advance, and thus the roll sheet may be deformed or lateral end portions of the roll sheet may be damaged. As a result, winding quality is degraded and irregularity of ends of the wound roll sheet is caused, which may possibly cause problems in subsequent steps.